Q: why can't i use italics?

Lucida Grande does not have an italic font, at least not the version installed on El Capitan.

Email is a text-only protocol. Anything not text must be encoded. To send font information, the message must be encoded with font info so that the receiving email client can determine what font info to use to display the message.

So, you can't tell it to create italicized text if the font information to create it does not exist.

In a word processor, you could tell the system to italicize anything and it will render some slanted text, and that program can send the slanted bits to a printer. However, Mail can't do the same thing via email.

As Barney said, you just need to use a font that does have an italic family.

None of those will affect the email you send. They are only for display at your end. You must set the message to Rich Text Format from the Format menu.

Then, Show Fonts from the Format menu and pick a font which has an Italic or Oblique font:

Abstractman23 wrote:

 

i don't seem to have SF UI on my imac.

Most people don't. FWIW, you should have marked Barney's reply as "Solved". Not mine.